SK279594B6 - Method and device for recycling plastic materials - Google Patents

Abstract

In a process for recycling plastic materials, the previously sorted plastic material wastes are comminuted, mixed, melted and homogenized during a first step, and then supplied to an injection and moulding device (13). The plastic material wastes are comminuted, mixed, melted and homogenized in a plasticator (10), and the raw materials thus recovered are immediately stocked in a storage chamber (12) wherein the raw materials are exposed, if necessary, to a regulated temperature, hence transporting said material into the injection and moulding device (13). A device consists of the plasticator (10) for comminution, mixing, melting and homogenisation of said wastes. The storage chamber (12), being adjacent to the plasticator, is connected to the injection and moulding device (13). Whenever, there is a mention of plastics, better-known "plastic materials" are understood under this term as well.

Description

The present invention relates to a process for the recycling of plastics in which the pre-sorted plastic waste is crushed, mixed, melted and homogenized in a first stage and subsequently fed to an injection and molding unit. The invention further relates to an apparatus for carrying out this method. Whenever plastics are referred to in any place, this is also understood to mean materials commonly known as 'plastics'.

BACKGROUND OF THE INVENTION

Said method and corresponding devices are already known in principle from published EP application no. 0321742. In a known device, an upright storage container is used. A crushing and mixing tool rotatable about the axis of the storage container and a sheath opening for discharging the granulate produced in the apparatus are disposed in the bottom region of the storage container. From there, the plastic material is transported to a two-stage screw conveyor or its temperature is adjusted.

Such a device does not ensure sufficient mixing so that the recycled material can also be used for the production of high-quality plastic products, nor does it make it possible to use an intermittent piston injection device due to the absence of intermediate storage.

Other methods and devices for recycling plastic waste are known from U.S. Pat. 2,382,655. In this case, the material is comminuted in a machine equipped with knives and subsequently transported by a screw conveyor for processing to another machine.

Further, U.S. Pat. No. 4,591,467, a two-stage mixing, heating and homogenizing of plastic materials is already known.

From DE patent no. 960854 is a known injection molding machine with a heated injection cylinder in which a permanently rotating screw is placed, by which the previously plasticized material is conveyed to the pressure space of the extruder. Such an injection molding machine is unusable for recycled material because it does not ensure sufficient mixing of the individual components.

Also from the utility model no. 1847590 is a known thermoplastic injection molding machine equipped with a screw plasticizer. The machine described herein is also unsuitable for recycled materials because it does not ensure sufficient mixing of the recycled components.

Plastics have become increasingly important not only in all areas of everyday life, but also in industry.

Meanwhile, there have also been increasing problems with the disposal of articles made of plastics, since, unlike natural materials or materials derived from natural materials, they do not undergo natural degradation and decomposition and do not return to the natural chain.

The meaning of plastics can be explained on the example of a car. The rapid development of the use of plastics and polymers has resulted in a 10% share of plastics in the car's weight. However, with this high rate of plastic introduction, they do not keep pace with the methods of reusing these modern materials. While steel, iron and aluminum, which account for approximately 75% of the vehicle's weight, are largely recovered, plastics only fill and load landfills. In addition, there is a risk that plastic parts, due to the aforementioned context, will gain an unfavorable reputation among the public and thus cease to be accepted by the population.

Finally, there is a danger that these modern materials will have to be replaced as far as possible by other materials for political reasons, although technicians would not like to give up using these materials, which, moreover, are difficult to replace in many parts.

Recycling of plastics is therefore a very topical problem. The path to plastic recycling is through dismantling and pre-sorting. By such a sorting, it is possible to obtain largely pure plastics. One of the big automakers therefore plans to build a dismantling plant in Wackersdorf. This is happening in the knowledge that without the recycling of plastics, the possibility of burning these plastics would have to be considered more seriously, but this would also be undesirable for environmental reasons.

With a view to recycling plastics, the largest industrial waste sorting plant in Europe is to be built in Berlin, with a capacity of approximately 100 000 tonnes of processed waste per year, which will be sorted into glass, metals, plastics and the like. The pre-sorted raw materials will then be ready for use as secondary raw materials.

A large amount of plastic waste comes mainly from the packaging industry. This waste is largely made up of only once heat-treated and high-quality plastics, since high-performance packaging production equipment can only work with the best materials.

The need for reuse of plastics has existed for a long time. However, all the projects put into practice so far have failed due to the very high costs of plastics treatment. The recycled material prepared by the hitherto known processes is therefore almost as expensive as the new material. This is, of course, a poor starting point for recycling, which in itself is absolutely necessary.

The reprocessed material is usually collected, sorted, milled and extruded in a preforming machine to produce a granulate, which is then re-melted at the processing plant to produce the desired products again. Repeated melting alone represents a considerable cost, resulting from high energy consumption.

A prerequisite for reuse of plastics is, in particular, sufficient pre-sorting. The choice of the intensity and quality of this sorting is governed by the purpose of the later use of the reprocessed material. Moreover, sufficient mixing of the pre-sorted material is necessary, since this material is not homogeneous in spite of the above-mentioned sorting, that is, the material is far from pure in terms of species. Significant proportions of polypropylene, for example closures, polystyrene, polyethylene terephthalate and the like, are also present in the feedstock, which mainly contains polyethylene.

Only good homogenization of the raw material will create the prerequisites for later re-utilization of plastics. It should also be possible to produce sophisticated products from the secondary raw material, possibly requiring the addition of additives and fillers such as talc, glass fibers, reinforcing agents in general, stabilizers and dyes.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and a construction of devices for carrying out this method, which makes it possible to produce full-value new plastics from recycled plastic material.

SUMMARY OF THE INVENTION

This problem is solved and the drawbacks of known methods and apparatus of this kind largely eliminated by a plastic recycling process in which the pre-sorted waste in the first stage is crushed, mixed, melted and homogenized and subsequently fed to an injection and molding unit according to the invention. consists in crushing, mixing, melting and homogenizing the plastic waste in a kneader, from which the raw material thus obtained is directly transported to a temperature-controlled buffer tank from which the raw material is fed to the injection unit. Whenever plastics are referred to in any place, this also means materials commonly known as 'plastics'.

It is advantageous if the feedstock is kept under an overpressure of up to 0.5 MPa during the intermediate storage in the buffer tank, and at the same time the degassing is also performed in the intermediate storage.

The essence of the apparatuses for carrying out the method is that the apparatus consists of a kneader for crushing, mixing, melting and homogenizing the waste, to which a buffer reservoir is connected to the intermediate storage, which is connected to the injection and shaping unit.

In this case, it is advantageous if the mixer is equipped with a degassing device and the buffer tank is designed as a temperature-controlled shaft.

Furthermore, it is advantageous if the buffer tank and / or the connecting pipe are also provided with the degassing device.

In some cases, it is further preferred that the buffer reservoir is equipped with a piston for forced material transport.

DETAILED DESCRIPTION OF THE INVENTION

The principle of the invention is further elucidated by means of an exemplary embodiment thereof, which is described with reference to the accompanying drawing, which shows a diagram of an apparatus for carrying out the method according to the invention.

The feedstock is first sufficiently swallowed if necessary and melted in a kneader 10, which in this sense constitutes a compounding unit. The mixing must be of sufficient intensity to ensure sufficient homogeneity of the raw material so treated. The kneader 10 thus also acts as a homogenizer, which mixes various substances, for example plastics, to which other additives may optionally be added, which is not in itself a subject of the invention. The kneading, melting and homogenization is achieved in the kneader 10 mainly by mechanical movement of a part of the kneader 10, which may be parallel, counter-rotating or axial and the like, achieved, for example, by rotors or screws, again not subject of the present invention until sufficiently mixed and plasticized raw materials. If desired, additional heating of the raw material to be processed can also be used, which is not a subject of the invention.

Only when sufficient mixing and plasticization is achieved, can the molten feedstock be passed through a connecting line 11 to a buffer tank or buffer tank 12, which may also be equipped with a controlled heating device, for example not shown, up, down and / or laterally positioned. channels, which in itself in this particular embodiment is not an object of the invention.

From the connecting pipe 11a of the buffer reservoir 12, the molten raw material flows further into the known injection and molding unit 13. This injection and molding unit 13 can be formed by a conventional screw extruder or also by a piston injection unit. invention.

A device for injecting hollow bodies can also be used. This type of equipment includes a continuously operating extruder for hollow products, an extruder with melt retention heads, wherein the extruder in the reservoir operates continuously, a blowing apparatus with extrusion screw-like aggregates similar to injection molding machines and operating batch and injection molding machines. in which a preform is blown, which is subsequently blown and which operate intermittently. These possible specific embodiments of the injection and molding unit 13 are not subject of the invention.

The feed region of the injection and molding unit 13 for injection molding or the screw (not shown) of the injection and molding unit 13 must be designed so that hot plasticized raw material can be drawn in. They must therefore be provided with a sufficiently large hole or the screw must have a sufficiently deep thread. It is also possible to use an injection and molding unit 13 with a piston (not shown). Also, these particular embodiments of the injection and molding unit 13 are not subject of the invention.

The dimensions of the individual units, i.e. the kneader 10, the connecting pipe 11, the buffer reservoir 12 and the injection and molding unit 13, are adapted to each other, so that the raw material flow through the entire device consisting of these units is as if continuous. A slight short-term fluctuation of the feedstock flow between said units is compensated by the buffer reservoir 12. This buffer reservoir 12 is also needed to ensure trouble-free interaction between the largely continuous kneader 10 and the injection molding unit 13, which operates intermittently. Long-term adaptation and monitoring of the feedstock flows in the individual units is provided by the central control unit 14, which can also influence and control the temperatures in the individual units of the plant.

The method and apparatus described are suitable not only for the reuse of plastic waste, but also for the simultaneous compounding and injection of new raw material mixtures, for example, for compounding polypropylene / mastic, polypropylene / glass fibers, polyamide / glass fibers, acrylonitrile / butadiene / styrene / dyes and the like.

The plastics and plastics blends can be mixed with one another, but also plastics or plastics blends with additives or fillers and thus processed into finished products.

An important advantage in the recycling of plastics according to the invention is the fact that a second melting is avoided in comparison with the conventional raw material pre-treatment and granulation. On the one hand, this not only reduces the energy costs to a significant degree, but also saves material.

For highly viscous plastics, a pressure increase of up to 0.5 MPa in the space of the buffer reservoir 12 may be required. This can be achieved by means of a piston (not shown) and the like, which is not in itself an object of the invention.

Said kneader 10 may advantageously be provided with a double screw (not shown). If, in a particular case, sufficient mixing of the raw material is achieved, a simple screw can also be used in the kneader 10. The kneader 10 may also be equipped with a degassing device.

The buffer reservoir 12 is preferably a tempered shaft. Also, this buffer tank 12 may be equipped with a degassing device. The buffer reservoir 12 may be provided for the free fall of the kneaded mass or may be provided with a device for forcibly conveying the mass, for example a piston (not shown). If necessary, this buffer reservoir 12 can also be designed for high pressures.

The injection and molding unit 13 which follows the described buffer reservoir 12 corresponds essentially to the state of the art and its construction is not the subject of the invention. As the injection and molding unit 13, it is possible to use known screw injection devices or piston injection devices.

Claims (8)

PATENT CLAIMS Process for recycling plastics, wherein the pre-sorted plastic waste is first comminuted, mixed, melted, homogenized and then fed to an injection and molding unit, characterized in that the plastic waste is comminuted, mixed, melted and homogenizing in a kneader (10) from which the raw material so obtained is directly transported to a temperature-controlled buffer tank (12) from where the raw material is fed to the injection and molding unit (13). Method according to claim 1, characterized in that the intermediate material is kept under an overpressure of up to 0.5 MPa when the intermediate material is stored in the buffer tank (12). Method according to claims 1 and 2, characterized in that the raw material is degassed in the buffer reservoir (12) during intermediate storage. Apparatus for carrying out the method according to claims 1 to 3 for recycling pre-sorted plastic waste which is crushed, mixed, melted and homogenised, characterized in that it comprises a kneader (10) for crushing, mixing, melting and homogenizing the waste to which, for intermediate storage, adjoins a buffer reservoir (12) which is connected to the injection and molding unit (13). Device according to claim 4, characterized in that the kneader (10) is equipped with a degassing device. Device according to claim 4, characterized in that the buffer reservoir (12) is designed as a temperature-controlled shaft. Device according to claims 4 to 6, characterized in that the buffer tank (12) and / or the connecting pipe (11) are equipped with a degassing device. Apparatus according to claims 4, 6 and 7, characterized in that the buffer reservoir (12) is equipped with a piston for the forced transport of material.